The present invention relates to the field of information storage and retrieval using integrated circuit technology. More specifically, the present invention relates to techniques for storing (and retrieving) analog or digital data, or both, within an integrated circuit using multilevel nonvolatile cells.
Among the most important and pioneering innovations in history are devices, techniques, and mediums that have been devised to record and playback sights, sounds, actions, and other information. Many of these innovations have led to the rise and growth of the media and entertainment industries, and also the personal and consumer electronics industries.
For example, among the most notable inventions are Thomas Alva Edison""s phonograph and record with which Edison recorded and played his first recording xe2x80x9cMary Had a Little Lamb.xe2x80x9d Other achievements in this field are the audio tape recorder, cassette tape recorder, motion picture, talking motion picture (xe2x80x9ctalkiesxe2x80x9d), video cassette recorder (VCR), compact disc (CD and CD-ROM), video disc, digital video disc (DVD), and many, many more of such innovations. In the present day, full-length motion pictures with stereo sound may be contained on a single optical disk.
Although these technologies have met with substantial success, there is a continuing desire to improve on the techniques, devices, mediums used to record information. For example, there is a need to provide techniques that provide dense storage of information. Denser storage facilitates storing information in a compact area, and provides a relatively long recording time.
There is a need to provide reliable and robust techniques. The stored reproduction should be a faithful reproduction of the original information. Despite repeated use, the stored reproduction should retain its original form, and also not degrade over time. Furthermore, the techniques should be compatible with and interface easily with present and emerging technologies in electronics and with devices facilitating electronic commerce (such as the Internet and World Wide Web).
Integrated circuit technology has been used to implement many electronic devices including computers, video recorders, digital cameras, microprocessors, DRAMs, SRAMs, Flash memory, and many others. As integrated technology continues to improve, it becomes practical to use this technology to record and playback sights, sounds, actions, and other information.
Data has typically been stored within integrated circuits using a digital or binary format. For applications where the input is analog, however, this requires conversion of signals to digital format, generally by an analog-to-digital (A/D) converter or similar means. And playback of analog signal from a digital storage format may require a digital-to-analog (D/A) converter or similar means. As can be appreciated, these conversions add complexity and extra expense to the entire procedure. Further, a conversion of the signal to digital form quantizes the signal and will lead to quantization noise in the reproduced signal.
Information such as sounds and voices, stereo and multichannel sounds, pictures, video, and others requires many bits of data storage. Storage of data in digital format may be inefficient because one bit (i.e., two different levels) of data is stored in a single memory cell. Further, it may be desirable to store an input signal using a sampling rate the user selects.
Therefore, techniques are needed for compactly storing (and retrieving) analog and digital information including sights, sounds, and actions using integrated circuit technology.
The present invention provides techniques for storing and retrieving analog or digital information from memory cells. In a specific embodiment, the memory cells are nonvolatile cells capable of analog or multilevel storage. Analog data and analog voltage levels are stored in the cells directly without the need for a conversion to digital form. Analog data is stored by altering a threshold voltage (VT) level of a memory cell to have a unique value representative of the analog data. A memory cell can also be used to store digital data. One or more digital bits can be stored in a single memory cell using a scheme consistent with the analog data storage.
Various different voltage levels are used to configure the memory cells. These voltage levels include high voltages, some of which may be at a level above the highest supply voltage for the integrated circuit. Some of these programming voltages are generated by a charge pump. These voltages are also shifted to a desired voltage level as needed to configure the memory cell to have a particular stored VT representative of the input data. The precision with which these programming voltages is obtained is important. Precise programming voltages are needed to ensure the memory cells are properly written, enhance the reliability and service life of the memory cells, and improve the yield of good die.
Changes in supply voltage or other parameters may affect the programming circuits and the voltage levels that are generated. In an embodiment of the present invention, the integrated circuit detects the voltage level of the supply voltage to the integrated circuit. Circuity on the integrated circuit such as the charge pump circuity adjusts to operate more effectively or efficiently at the voltage level of the supply voltage.
In an embodiment, a technique of the present invention includes detecting an external voltage to the integrated circuit to determine whether the external voltage is above or below a threshold value. When the external voltage is below the threshold value, a programming voltage is generated using a first number of charge pump stages. When the external voltage is above the threshold value, the programming voltage is generated using a second number of charge pump stages, where the second number of charge pump stages is less than the first number of charge pump stages.
In another embodiment, a technique of the present invention includes detecting an external voltage to the integrated circuit to determine whether the external voltage is above or below a first threshold level and above or below a second threshold level, where the second threshold level is above the first threshold level. When the external voltage is below the first threshold level, a programming voltage is generated using a first number of charge pump stages. When the external voltage is above the first threshold level and below the second threshold level, the programming voltage is generated using a second number of charge pump stages. When the external voltage is above the second threshold level, the programming voltage is generated using a third number of charge pump stages, where the first number of charge pump stages is greater than the second number of charge pump stages, and the second number of charge pump stages is greater than the third number of charge pump stages.
The present invention includes an integrated circuit with a first voltage detect circuit of a first threshold level, a second voltage detect circuit of a second threshold level, and a third voltage detect circuit of a third threshold level. A logic circuit, connected to outputs of the first, second, and third voltage detect circuits, generates a number of enable outputs. A charge pump circuit includes a number of stages, and based on the enable outputs, a number of stages of the charge pump are enabled.
In a specific embodiment, a voltage detect circuit includes a first transistor connected between a first voltage detect output node and first terminals of a first and a second capacitor. A control electrode of the first transistor is connected to a clock signal. A second transistor is connected between the first voltage detect output node and the first terminals of the first and second capacitors. A control electrode of the second transistor is connected to the clock signal. A first switch circuit connected between an external voltage input and a second terminal of the first capacitor. A second switch circuit is connected between a reference voltage input and a second terminal of the second capacitor.
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the figures.